The invention relates to a method for functionally testing a vehicle dynamics control sensor system of a vehicle, which comprises a yaw rate sensor, a transverse acceleration sensor and/or a steering angle sensor.
In modern motor vehicles, vehicle dynamics control systems are increasingly used to support the driver specifically in situations which are critical for vehicle dynamics, in particular by means of situation-dependent, wheel-specific braking intervention. A precondition for this is the detection of the current state of vehicle dynamics using a vehicle dynamics control sensor system, which contains one or two or all three of the abovementioned sensors. In many earlier vehicle dynamics control systems, the associated sensor system is composed, for example, of a yaw rate sensor and a steering angle sensor, while in modern vehicles all three abovementioned sensors are used. Vehicle dynamics control systems of this type are used, for example, by DaimlerChrysler AG in its vehicles under the abbreviation ESP (Electronic Stability Program).
As in all vehicle components, the vehicle dynamics control sensor system is also subject to possible malfunctions, which may be due to a failure of the sensor or sensors or due to faulty installation of the sensor system. The following are examples of sources of faults: interchanging of yaw rate sensor and transverse acceleration sensor; cable twisting on the cabling of the yaw rate sensor and/or on the cabling of the transverse acceleration sensor; incorrect installation position of the yaw rate sensor and/or of the transverse acceleration sensor; emission of a constant, xe2x80x9cstuckxe2x80x9d signal of one of the sensors despite its electrical part being free of faults; and incorrect repair to the steering angle sensor or to the vehicle steering system.
It is therefore necessary to have a method with which the functional capability of the vehicle dynamics control sensor system can be checked for freedom from faults, in particular before the vehicle is first put into service and after repairs.
U.S. Pat. No. 5,617,337 describes a method and a device for functionally monitoring a sensor for sensing a measured value in a motor vehicle. When predefined operating states are present, a measured value is sensed and compared with a reference value. Faults are detected if a measured value which is made available by the sensor differs from a reference value by more than a tolerance value. A measured value, which has been registered at an earlier time at a corresponding operating state and has been stored, serves as reference value. The sensor is a sensor for registering the position of a control rod of a diesel injection pump. In the operating state under consideration, the control rod is, for example, in a stop limit position or in a start limit position.
In the German laid-open application DE 196 36 443 A1, a method for functionally testing a vehicle dynamics control sensor system of a vehicle is described which has a yaw rate sensor, a transverse acceleration sensor and a steering angle sensor. Comparison variables, defined in the same way, are determined for the individual sensors of the vehicle dynamics control sensor system as a function of the signals generated by them. In accordance with the exemplary embodiment described, for example, a yaw rate is determined as a comparison variable for the transverse acceleration sensor as a function of the transverse acceleration signal generated by it. The same applies to the steering angle sensor and to the wheel speed sensors. A reference variable is then determined from the comparison variables which are defined in the same way for the respective sensors. The exemplary embodiment here is also concerned with a yaw rate. Using inverse mathematical models, in each case a sensor reference variable is determined at least for some of the sensors as a function of the reference variable. The individual sensor is then checked as a function of this sensor reference variable, using plausibility interrogations.
Accordingly, the technical problem on which the invention is based is to make available a method of the type mentioned at the beginning with which the function of a vehicle dynamics control sensor system can be checked reliably and relatively easily.
The invention solves this problem by making available a method that, initially at the start of a test process, the measurement signal values of the vehicle dynamics control sensor system which are present at this moment are sensed as corresponding starting values. Then, during a subsequent test run of the vehicle, which takes place under predefinable test run conditions, the measurement signal values, which are continuously supplied by the vehicle dynamics control sensor system, are compared with the associated starting values. Here, the test run includes, in particular, travelling through a bend with a vehicle longitudinal speed which lies in a predefinable speed range. For such a driving situation, the measurement signals of the respective sensor or sensors lie within characteristic ranges under no fault conditions. By subsequently evaluating the results of comparing the measurement signal values, which are obtained during the test run, with the associated starting values, it is possible to detect whether the vehicle dynamics control sensor system is operating without faults. Only when the system is operating without faults, the comparison results lie within predefinable value ranges which can depend on the test run conditions. It becomes apparent that reliable functional testing of the vehicle dynamics control sensor system can be achieved by means of this procedure.
In another method according to the present invention, which is suitable for a vehicle dynamics control sensor system which comprises a yaw rate sensor, a transverse acceleration sensor and a steering angle sensor, compliance with a cornering condition for the test run is monitored by reference to the output signals of the three sensors. It is known that each of these three sensors is suitable for detecting cornering. According to the invention, it is therefore concluded that cornering is actually occurring if at least two of the three sensors indicate such a cornering situation.
In yet another method according to the present invention, the test run conditions are selected in terms of the longitudinal speed of a vehicle such that the longitudinal speed lies within a relatively low speed range. For this speed range, well-defined relationships are obtained between the individual sensor signals to facilitate the testing for the freedom of the sensors from faults. In this low speed range, for example, a test run normally always results in a higher measurement signal value for the yaw rate sensor than for the transverse acceleration sensor.
In a further method according to the present invention, the steering angle sensor, which can be specifically a steering wheel angle sensor, for example, is checked for freedom from faults by detecting whether the measured steering angle value registered by the sensor during the test run lies, on at least one occasion, above the associated steering angle starting value in absolute terms by more than a predefined minimum value. This is a suitable criterion for the functional capability of the steering angle sensor taking into account the fact that the vehicle travels through a bend during the test run and this is expressed in a corresponding change in the steering angle.
One development of the inventive method according to claim 5 relates specifically to functional checking of yaw rate and transverse acceleration sensors. Here, the ratio between the two differences between the current measurement signal value and the associated starting value is determined for the two sensors and it is subsequently tested whether said ratio lies within a predefinable set point range. If not, it is concluded that there is a malfunction in one of the two sensors, in which case the term xe2x80x9csensor malfunctionxe2x80x9d is to be understood here as not only a sensor failure but also, for example, incorrect cabling of the respective sensor. This procedure exploits the fact that in a fault-free situation under the given test run conditions there is a certain correlation between the measurement signals of these two sensors, which correlation is reflected in the fact that the aforesaid ratio then lies in the associated set point range.
A method which is developed according to claim 6 is suitable for functionally testing in particular the yaw rate sensor and/or the transverse acceleration sensor, and said method provides for the absolute value of the difference between the current measurement signal value and the associated starting value to be determined repeatedly for the respective sensor of the two sensors during the test run, and for the presence of a malfunction in the respective sensor to be concluded if this absolute value of the difference lies too rarely above a minimum value over the entire duration of the test run. This procedure exploits the fact that when there are no faults, these sensors supply, during the cornering which follows the vehicle starting state, a measurement signal value which is sufficiently different from the starting value, which possibly changes continuously and which neither remains constant with respect to the starting value over a relatively long time period nor merely changes suddenly during the test run.
One advantageous embodiment of the invention is illustrated in the drawings and will be described below. In said drawings: